Multi-layer circuit boards contain and/or include electrical components which selectively and operatively populate opposed first and second surfaces (i.e., top and bottom surfaces) of each board (or other respective interior portions of each of the boards), thereby desirably allowing each of the electrical circuit boards to contain and/or include a relatively large amount of electrical components which efficiently and densely populate the respective boards.
It is desirable to allow for communication by and between and/or interconnection of the component containing surfaces and/or portions of an electrical circuit board, thereby allowing the contained electrical components on each side of the board (or within certain interior portions of the board) to cooperatively and selectively interconnect to form one or more desired electrical circuits. This communication and interconnection may require the use of shared electrical ground planes, the transmittal of electrical power and/or control type signals between each of the component containing surfaces and/or the component containing board portions, and/or the selective and physical connection of various contained components.
This desired interconnection typically requires one or more holes or cavities to be drilled and/or formed through one or more layers of the circuit board, thereby selectively creating one or more vias (i.e., holes which pass through some or all of the opposed component containing surfaces) which can be used to selectively connect various portions or layers of the circuit board. The vias are then typically filled with solder (e.g., a pin or component connector is soldered into the hole) In this manner, electrical connections are made or formed which connect electrical components and/or circuitry to the core of the circuit board substrate, to other circuit board layers, or to other components and/or circuitry located on the opposing side or surface of the board.
One drawback with these conventional vias is that layers of relatively non-solderable material (i.e., material which does not substantially bind or metallurgically bond with solder) are typically present within these vias, and thus, the solder does not consistently and reliably electrically connect the desired layers of circuitry and/or components together. For example and without limitation, many conventional multi-layer circuit boards include adhesive material or film which is used to couple portions of the circuit boards together. This adhesive film or material is often disposed adjacent to or in relative close proximity to a via and often softens and flows into the via when the circuit board substrate is laminated, thereby causing soldering defects in the subsequent circuit board construction processes. For example and without limitation, the adhesive which flows into the via often flows over or covers portions of the conducting surfaces or layers within the via (e.g., the bottom layer or surface of the via), thereby often preventing the solder from “wetting” or metallurgically bonding to the core or bottom layer of the circuit board. This results in a defective portion or region of the circuit board where all layers of the circuit board are not desirably interconnected.
There is therefore a need for a multi-layer electrical circuit board which overcomes some or all of the previously delineated drawbacks of prior circuit boards and which includes improved vias or cavities for selectively interconnecting one or more layers of electrical circuitry.